In the manufacture of semiconductor devices, certain coating processes are performed by chemical vapor deposition (CVD). The two general types of CVD processes are blanket and selective CVD. In blanket CVD, desired film coatings are deposited over the entire exposed surface of the semiconductor wafer. In selective CVD, desired film coatings are applied to the exposed surfaces of the contact or via holes which pass through the insulative layers on the semiconductor wafers; e.g., to provide plugs of conductive material for the purpose of making interconnections across the insulating layers.
Frequently, the desired ultimate result of CVD processes is for filling holes or vias and for forming interconnections between layers on semiconductor wafers. This can be accomplished in one of two ways: 1) formation of the desired film coating on only selected portions of the wafer surfaces by selective deposition; and 2) blanket film deposition with subsequent etching. Because direct selective application by CVD of film coatings may be unreliable, unsuccessful, and/or slow, and thus undesirable on a commercial scale where rapid throughput and efficient use of expensive machinery is important, selective coatings are often achieved by blanket deposition and subsequent etching back from the areas where permanent coating is not desired. When utilizing blanket CVD followed by etching back of the deposited material, a high degree of thickness uniformity in the blanket coating is required, particularly in the areas where the deposited material is to be etched. If the film coating thickness is irregular in the etched-back areas, the etching process may selectively damage the underlying layers or may result in regions where residual coating remains. Known blanket CVD processes of the prior art have coated substrates with limited uniformity and/or at limited speed. Accordingly, processes for the application of blanket coatings of acceptable thickness uniformity and at relatively higher speeds are required.
To uniformly apply coatings such as tungsten (W) by CVD to semiconductor wafers, it is desirable to ensure a uniform supply of reactant gases across the surface of the wafer, and to uniformly remove spent gases and reaction by-products from the surfaces being coated. In this regard, prior art CVD processes perform with limited success. Accordingly, there is a need for processes which more efficiently and more uniformly supply reaction gases to and remove reaction by-products from the surfaces of wafers being coated in CVD processes, either blanket or selective.
In CVD processes using known reactors, turbulence in the flow of reaction gases has inhibited the efficiency and uniformity of the coating process and has aggravated the deposition and migration of contaminants within the reaction chamber. Accordingly, there is a need for CVD processes which have improved gas flow and reduced gas flow turbulence.
In both selective and blanket CVD processes, particularly tungsten CVD processes, tungsten hexafluoride (WF.sub.6) is employed as a reactant gas. Tungsten hexafluoride is very costly and thus when reactant gas utilization efficiency is low, as in many prior art processes, the overall process costs are significantly increased. For example, some prior art CVD processes are believed to have a utilization efficiency of WF.sub.6 as low as about 20% or less, and thus the cost of WF.sub.6 often exceeds 30% of the overall cost of the CVD process. Accordingly, CVD processes that are more efficient in the consumption (conversion) of reactant gases, such as WF.sub.6, are desired.
The use of rotating disk CVD reactors to achieve improved control of the deposited film properties on flat, unpatterned substrates has been shown. It has been demonstrated that good thickness uniformity across the diameter of an entire wafer is achievable using a rotating disk reactor due to the ability to control the boundary layer thickness across the entire wafer surface. Such boundary layer thickness control is a fundamental feature of the geometry of rotating disk systems. In contrast, other known types of reactors commonly used in CVD to deposit thin films on silicon wafers have a continuously changing boundary layer across a given wafer in the direction of gas flow. Epsilon Technology, Inc. has shown the efficacy of using rotating disk reactors for epitaxial silicon CVD on silicon wafers. However, it is believed that none of this prior work has been practiced on patterned wafers, and thus uniform deposition of high quality films onto wafers which fill the patterned holes or vias, whether by blanket or selective deposition, has never been demonstrated. Accordingly, CVD processes for selective and blanket deposition of conductive layers on patterned semiconductor substrates which exhibit uniform thickness, good step coverage, uniform resistivity and other desirable film qualities are required.